In one of Stanford University's laboratories, a discovery has been made that rewrites two centuries of biological assumptions. Researchers analyzed the earliest stages of mouse embryo development and found something astonishing: two completely different genetic programs govern the birth of the anterior and posterior regions of the brain. One route activates the Otx2 gene and leads to the formation of the forebrain and midbrain. The other involves Gbx2 and sets the development of the hindbrain. Especially important: these lines develop in parallel and hardly intersect, like two trains launched onto different tracks.
Already at the gastrulation stage — one of the earliest stages of embryonic development — cells diverge in their fate. Their molecular programs differ so early that it resembles tickets to different carriages issued to passengers before departure. Molecular analyses of chromatin (the material that packages DNA) showed that the anterior and posterior neural ectoderm have fundamentally different configurations already at these early stages — as if different architectural blueprints were encoded in the very foundations of development.
For decades, a completely different model prevailed: scientists believed that the entire brain forms from a single group of progenitor cells, and that differences between its regions arise later, as differentiation proceeds. A new paper published on 18 September 2026 in the journal Nature Neuroscience, seriously revises this picture of the world.
The study was led by Kyle Loh, an assistant professor in the Department of Developmental Biology at Stanford University, in collaboration with graduate students Caroline Dundes and Ryan Johai. They discovered that the anterior regions of the brain and the hindbrain follow different embryonic trajectories from the earliest stages, and these paths never converge again.
The forebrain is what makes us human. It is responsible for perception and orientation in space, memory, language, planning, and all complex thinking, including metacognition and self-awareness. The hindbrain is an ancient core inherited from our ancestors. It participates in maintaining vital functions: breathing, heartbeat, swallowing, movement, coordination. It is what the brain does automatically, without the involvement of consciousness.
Therefore the brain ceases to look like a single structure that first arises as a whole and then divides into specialized parts. Instead, it appears as a complex composite organ — something like two ancient nervous systems that evolution once glued into a single mechanism, packed into one skull.
This is precisely where the discovery becomes critically important for the study of consciousness — a question that has tormented philosophers and neuroscientists for thousands of years.
Let's take Giulio Tononi's integrated information theory. It proposes that consciousness arises from a high degree of integration of causally connected elements of a system. But if different parts of the brain have such different embryonic origins, split apart and sealed off at the molecular level, an additional question arises: is integration an original property of the nervous system, or does it gradually appear as different neural systems learn to interact and hear one another?
A similar paradox arises within the framework of the global neuronal workspace theory, developed by Bernard Baars and Stanislas Dehaene. These scientists propose that consciousness arises when information acquires global access, when it is broadcast throughout the brain like an announcement in the main square. But if the forebrain and the hindbrain develop independently, is it possible that the complex mechanisms of global information propagation arose not within an initially homogeneous system, but as a way of coordinating already existing, deeply different neural modules?
It is important to emphasize: the study itself did not test these theories of consciousness. But these findings make the theories especially interesting to rethink, especially for those who seek new answers to old questions.
The methodology of the work was thorough and multi-level. The researchers tracked gene expression and cell lineages in living mouse embryos, analyzed chromatin states, and then moved on to human pluripotent stem cells — cells that can turn into any type of tissue.
But the most impressive result came from the practical part of the study.
The researchers managed to do what scientists had failed to do for decades: they successfully directed human pluripotent stem cells into functional motor neurons of the hindbrain. And these were not merely cells that resembled neurons by molecular markers. They generated action potentials — the very electrical impulses that run along nerves, making muscles work. They behaved like living, functional nerve cells.
The authors, meanwhile, remain scientists and stay cautious. It is still impossible to fully rule out the existence of a very brief common predecessor at even earlier stages of development. So to speak of the absolute independence of the two lines would be premature. Science demands humility before the unknown.
The evolutionary scale of the discovery turned out to be unusually broad.
The researchers found similar parallel developmental pathways not only in mammals, but also in chickens, in zebrafish (striped little fish, a favorite of geneticists) and even in Saccoglossus kowalevskii — a small acorn worm from the hemichordate group, which soon became the main hero of the story of vertebrate evolution.
Humans and these animals shared a common ancestor more than 550 million years ago — in the Cambrian period, when life on Earth was young and wild. This suggests that such a division of the nervous system arose very long ago — even before the appearance of vertebrates in their modern form, and was then inherited and preserved by all their descendants.
The practical significance of the work is hard to overestimate, especially for medicine.
For a long time, researchers faced a mystery: why is it impossible to obtain full-fledged hindbrain neurons from forebrain precursors? Some attempts seemed a waste of time. Now everything has fallen into place: perhaps the problem lay not in the method, but in the starting material. It is as if you were trying to convert a residential neighborhood into an industrial complex when the very architecture of the building was already determined at the stage of the foundation — no methods and no money will help remake what is baked in genetically.
The new approach may help create more accurate laboratory models of devastating diseases. Amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA) — these are two enemies from which motor neurons suffer, causing paralysis and impaired breathing. Now scientists have a chance to recreate these diseases in a Petri dish, understand their mechanisms and find drugs.
And yet the most intriguing question remains beyond embryology itself.
If the forebrain and the hindbrain really do develop as two ancient biological routes that then unite into a single nervous system, then the nature of consciousness begins to look radically different.
Perhaps the question of where the "center" of consciousness is located — in the cortex, in the thalamus, or somewhere else — is not so important after all.
It is no less important to understand how two profoundly different neural systems, formed by different evolutionary programs and different embryonic paths, learned to speak to each other so well that we — the only known animals capable of being aware of ourselves — perceive their joint work as a single, indivisible, whole "I."
